In order to verify whether rule size affects rule following, 16 college students were exposed to a matching-to-sample procedure. Depending upon the sample three comparisons should be pointed in a different sequence. Correct sequencing was reinforced. Each condition had three sessions with 30 trials each, and started with one of three rules. Under Condition I, minimal instructions were given; under Condition II, rules R1, R2, and R1 were used, in this sequence; under Condition III, rules R2, R1, and R2 were used, in this sequence; and under Condition IV, rules R3, R1, and R3 were used, in this sequence. R3 was longer than R2, and R2 was longer than R1. Results showed that Rules 1 and 2 were always followed. Rule 3 was followed only in the third session, Condition IV. It is suggested that the size and complexity of a rule does affect rule following behavior.